Vibrational And Structural Signatures Of The Crossover Between Dense Glassy And Sparse Gel-Like Attractive Colloidal Packings,
2014
University of Pennsylvania
Vibrational And Structural Signatures Of The Crossover Between Dense Glassy And Sparse Gel-Like Attractive Colloidal Packings, Matthew A. Lohr, Tim Still, Raman Ganti, Matthew D. Gratale, Zoey S. Davidson, Kevin B. Aptowicz, Carl P. Goodrich, Daniel M. Sussman, A. G. Yodh
Physics & Engineering Faculty Publications
We investigate the vibrational modes of quasi-two-dimensional disordered colloidal packings of hard colloidal spheres with short-range attractions as a function of packing fraction. Certain properties of the vibrational density of states (vDOS) are shown to correlate with the density and structure of the samples (i.e., in sparsely versus densely packed samples). Specifically, a crossover from dense glassy to sparse gel-like states is suggested by an excess of phonon modes at low frequency and by a variation in the slope of the vDOS with frequency at low frequency. This change in phonon mode distribution is demonstrated to arise largely from localized …
Ferroelectric Tunnel Junctions With Graphene Electrodes,
2014
University of Nebraska-Lincoln
Ferroelectric Tunnel Junctions With Graphene Electrodes, Haidong Lu, Alexey Lipatov, Sangjin Ryu, D. J. Kim, H. Lee, M. Ye. Zhuravlev, Chang-Beom Eom, Evgeny Y. Tsymbal, Alexander Sinitskii, Alexei Gruverman
Evgeny Tsymbal Publications
Polarization-driven resistive switching in ferroelectric tunnel junctions (FTJs)—structures composed of two electrodes separated by an ultrathin ferroelectric barrier—offers new physics and materials functionalities, as well as exciting opportunities for the next generation of non-volatile memories and logic devices. Performance of FTJs is highly sensitive to the electrical boundary conditions, which can be controlled by electrode material and/or interface engineering. Here, we demonstrate the use of graphene as electrodes in FTJs that allows control of interface properties for significant enhancement of device performance. Ferroelectric polarization stability and resistive switching are strongly affected by a molecular layer at the graphene/BaTiO3 interface. …
Electrostatic Breakdown Analysis,
2014
Utah State University
Electrostatic Breakdown Analysis, Sam Hansen
Senior Theses and Projects
Materials potentially suitable for spacecraft construction were exposed to electrostatic discharge in the USU Materials Physics Group lab, with hopes of identifying samples that possess greater resistance to breakdown. Breakdown shape and size may be important to determining material suitability for spacecraft construction [1]. The discharge damage sites of tested samples were examined, measured and logged into a matrix file for data analysis. Once logged, data was sorted within the matrix and compared graphically to identify trends.
Electrostatic Breakdown Analysis,
2014
Utah State University
Electrostatic Breakdown Analysis, Sam Hansen, Jr Dennison, Allen Andersen
Senior Theses and Projects
Materials potentially suitable for spacecraft construction were exposed to electrostatic discharge in the USU Materials Physics Group lab, with hopes of identifying samples that possess greater resistance to breakdown. Breakdown shape and size may be important to determining material suitability for spacecraft construction [1]. The discharge damage sites of tested samples were examined, measured and logged into a matrix file for data analysis. Once logged, data was sorted within the matrix and compared graphically to identify trends.
Nonlinear Optimal Filter Technique For Analyzing Energy Depositions In Tes Sensors Driven Into Saturation,
2014
Hope College
Nonlinear Optimal Filter Technique For Analyzing Energy Depositions In Tes Sensors Driven Into Saturation, Benjamin Shank, Jeffrey Yen, Blas Cabrera, John Mark Kreikebaum, Robert Moffatt, Peter Redl, Betty Young, Paul Brink, Matthew Cherry, Astrid Tomada
Faculty Publications
We present a detailed thermal and electrical model of superconducting transition edge sensors(TESs) connected to quasiparticle (qp) traps, such as the W TESs connected to Al qp traps used for CDMS (Cryogenic Dark Matter Search) Ge and Si detectors. We show that this improvedmodel, together with a straightforward time-domain optimal filter, can be used to analyze pulses well into the nonlinear saturation region and reconstruct absorbed energies with optimal energyresolution.
Control Of Majorana Edge Modes By A G-Factor Engineered Nanowire Spin Transistor,
2014
University of California, Riverside
Control Of Majorana Edge Modes By A G-Factor Engineered Nanowire Spin Transistor, Amrit De, Alexey Kovalev
Department of Physics and Astronomy: Faculty Publications
We propose the manipulation of Majorana edge states via hybridization and spin currents in a nanowire spin transistor. The spin transistor is based on a heterostructure nanowire comprising of semiconductors with large and small g-factors that form the topological and non-topological regions respectively. The hybridization of bound edge states results in spin currents and 4π-periodic torques, as a function of the relative magnetic field angle – an effect which is dual to the fractional Josephson effect. We establish relation between torques and spin-currents in the non-topological region where the magnetic field is almost zero and spin is …
Fate Of The Bose Insulator In The Limit Of Strong Localization And Low Cooper-Pair Density In Ultrathin Films,
2014
University of New Hampshire - Main Campus
Fate Of The Bose Insulator In The Limit Of Strong Localization And Low Cooper-Pair Density In Ultrathin Films, Shawna M. Hollen, G. E. Fernandes, J. M. Xu, J M. Valles Jr.
Physics & Astronomy
A Bose insulator composed of a low density of strongly localized Cooper pairs develops at the two-dimensional superconductor to insulator transition (SIT) in a number of thin film systems. Investigations of ultrathin amorphous PbBi films far from the SIT described here provide evidence that the Bose insulator gives way to a second insulating phase with decreasing film thickness. At a critical film thickness dc the magnetoresistance changes sign from positive, as expected for boson transport, to negative, as expected for fermion transport, signs of local Cooper-pair phase coherence effects on transport vanish, and the transport activation energy exhibits a kink. …
Pre-Breakdown Arcing And Electrostatic Discharge In Dielectrics Under High Dc Electric Field Stress,
2014
Utah State University
Pre-Breakdown Arcing And Electrostatic Discharge In Dielectrics Under High Dc Electric Field Stress, Allen Andersen, Jr Dennison
Journal Articles
Highly disordered insulating materials exposed to high electric fields will, over time, degrade and fail, potentially causing catastrophic damage to devices. Step-up to electrostatic discharge (ESD) tests were performed for two common polymer dielectrics, low density polyethylene and polyimide. Pre-breakdown transient current spikes or arcs were observed, using both slow and high speed detection. These pre-ESD discharge phenomena are explained in terms of breakdown modes and defect generation on a microscopic scale. The field at which pre-breakdown arcing begins was compared to the onset field for electrostatic discharge at which complete breakdown occurs for each material studied. We present evidence …
Pre-Breakdown Arcing And Electrostatic Discharge In Dielectrics Under High Dc Electric Field Stress,
2014
Utah State University
Pre-Breakdown Arcing And Electrostatic Discharge In Dielectrics Under High Dc Electric Field Stress, Allen Andersen, Jr Dennison
Conference Proceedings
Highly disordered insulating materials exposed to high electric fields will, over time, degrade and fail, potentially causing catastrophic damage to devices. Step-up electrostatic discharge (ESD) tests were performed for two common polymer dielectrics, low density polyethylene and polyimide. Prebreakdown transient current spikes or pre-arcs were observed, using both slow and high speed detection. These pre-ESD discharge phenomena are explained in terms of breakdown modes and defect generation on a microscopic scale. The field at which pre-breakdown arcing begins was compared to the onset field for electrostatic discharge at which complete breakdown begins to occur for each material. We present evidence …
Modeling The Energy Dependent Cathodoluminescent Intensity Of A Carbon Composite Material,
2014
Utah State University
Modeling The Energy Dependent Cathodoluminescent Intensity Of A Carbon Composite Material, Justin Christensen, Kelby T. Peterson, Justin Dekany, Jr Dennison
Presentations
When highly disordered insulating materials are subjected to energetic electron bombardment they can emit photons. This process is termed “cathodoluminescence.” This occurs in the space plasma environment and is an important phenomenon to understand when designing any object to be put into space. Light emitted from spacecraft materials can affect optical detection, and can cause stray-light contamination in space-based observatories. The Materials Physics Group at Utah State University uses an ultra-high vacuum chamber equipped with electron guns and a cryostat to control the sample temperature to simulate the space environment and to observe its affects on sample materials. Previous studies …
Discharge Breakdown Analyses,
2014
Utah State University
Discharge Breakdown Analyses, Sam Hansen, Jr Dennison, Allen Andersen
Presentations
Material breakdown due to Electrostatic discharge (ESD) is the primary cause of spacecraft damage due to environment interactions in space. This occurs when the space plasma fluxes charge a craft to high voltages where insulating craft materials then break down. This failure allows current to flow freely through the material, this can damage or destroy onboard electrical systems. My project focuses on the effects of these breakdowns on suspect materials commonly used for electrical insulation in space. The USU Material Physics Group has performed ESD tests on hundreds of samples to date. The ESD damage sites of these samples have …
Lifetimes Of Polymeric Dielectrics: A Dual-Defect Model,
2014
Utah State University
Lifetimes Of Polymeric Dielectrics: A Dual-Defect Model, Allen Andersen, Jr Dennison
Presentations
Electrostatic discharge (ESD) can cause catastrophic failures in electronic devices. Estimating the lifetime of dielectrics under prolonged high field exposure is a major design concern for applications including spacecraft, high voltage DC power transmission, and semiconductor electronics. Dielectric strengths listed in engineering handbooks are primarily based on cursory measurements with poor repeatability and tend to overestimate ESD fields in real applications. Standard measurements subject test samples to ~500 V/s ramp rates until breakdown. We present the results of ESD studies in two prototypical polymer dielectrics using a ramp rate of ~20 V/4s until breakdown together with tests applying a static …
Cathodolumiescence Studies Of The Density Of States Of Disordered Silicon Dioxide,
2014
Utah State Univesity
Cathodolumiescence Studies Of The Density Of States Of Disordered Silicon Dioxide, Jr Dennison, Amberly Evans Jensen
Presentations
Electron bombardment measurements have shown that disordered SiO2 exhibits cathodoluminescence, with an overall intensity that varies with incident electron beam energy and current density, sample temperature, exposure time, and wavelength. A simple model based on the defect density of states—used to explain electron transport in highly disordered insulating materials—has been extended to predict the relative cathodoluminescent intensity and spectral radiance for disordered SiO 2 as a function of these variables. The spectral radiance exhibited four distinct bands, corresponding to four distinct energy distributions of defect states within the band gap; each showed different temperature dependence. These localized defect or “trap” …
Space Effects Survivability Testing,
2014
Utah State University
Space Effects Survivability Testing, Lisa Montierth Phillipps, Jr Dennison, Kent Hartley, Robert H. Johnson, Justin Dekany, James S. Dyer
Presentations
A versatile test facility has been designed to study the effects of space environment fluxes and radiation damage on small scale materials samples, system components, and small satellites. Cost-effective long-duration testing for potentially environmental-induced modifications is increasingly more important as small satellite programs have longer mission lifetimes, expand to more harsh environments, make more diverse and sensitive measurements, minimize shielding to reduce mass, and utilize more compact and sensitive electronics. The facility simulates environmental components including the neutral gas atmosphere, the solar spectrum, electron plasma fluxes, and temperature. The UV/VIS/NIR solar spectrum is simulated using a class AAA Solar Simulator …
Cathodoluminescence Events Coincident With Muon Detection,
2014
Utah State University
Cathodoluminescence Events Coincident With Muon Detection, Kenneth Zia, Justin Dekany, Jr Dennison
Presentations
Samples of highly disordered insulating material have been irradiated with keV electron beams, resulting in three forms of electron induced light emission with differing duration: arcs (duration), “flares” (~100 s), and cathodoluminescence (as long as beam is on) [Dennison, 2013]. The arc and cathodoluminescence phenomena are well understood, while the flares’ origins are not. Flares were observed at intervals of ~2 per hr. This is within a factor of 2 for the expected muon cross section at an altitude of Logan, UT (1370 m) caused by high altitude cosmic rays; those high energy particles could have deposited sufficient energy throughout …
Cathodoluminescence Events Coincident With Muon Detection,
2014
Utah State University
Cathodoluminescence Events Coincident With Muon Detection, Kenneth Zia
Senior Theses and Projects
No abstract provided.
Complex Band Structure Of Topologically Protected Edge States,
2014
University of Nebraska-Lincoln
Complex Band Structure Of Topologically Protected Edge States, Xiaoqian Dang, John D. Burton, Alan Kalitsov, Julian P. Velev, Evgeny Y. Tsymbal
Evgeny Tsymbal Publications
One of the great successes of modern condensed matter physics is the discovery of topological insulators (TIs). A thorough investigation of their properties could bring such materials from fundamental research to potential applications. Here, we report on theoretical investigations of the complex band structure (CBS) of two-dimensional (2D) TIs. We utilize the tight-binding form of the Bernevig, Hughes, and Zhang model as a prototype for a generic 2D TI. Based on this model, we outline the conditions that the CBS must satisfy in order to guarantee the presence of topologically protected edge states. Furthermore, we use the Green’s function technique …
Guesstimation: The Art Of Getting About The Right Answer,
2014
Utah State Univesity
Guesstimation: The Art Of Getting About The Right Answer, Jr Dennison
Presentations
No abstract provided.
A Dual-Defect Model For Predicting Lifetimes For Polymeric Discharges From Accelerated Testing,
2014
Utah State University
A Dual-Defect Model For Predicting Lifetimes For Polymeric Discharges From Accelerated Testing, Allen Andersen, Jr Dennison
Posters
Electrostatic discharge (ESD) can cause catastrophic failures in electronic devices. Estimating the lifetime of dielectrics under prolonged high field exposure is a major design concern for applications including spacecraft, high voltage DC power transmission, and semiconductor electronics. Dielectric strengths listed in engineering handbooks are primarily based on cursory measurements with poor repeatability and tend to overestimate ESD fields in real applications. Standard measurements subject test samples to ≈500 V/s ramp rates until breakdown. We present the results of ESD studies in two prototypical polymer dielectrics using a ramp rate of ≈20 V/4s until breakdown, together with tests applying a …
Cathodolumiescence Studies Of The Density Of States Of Disordered Silicon Dioxide,
2014
Utah State Univesity
Cathodolumiescence Studies Of The Density Of States Of Disordered Silicon Dioxide, Jr Dennison, Amberly Evans Jensen
Presentations
Electron bombardment measurements have shown that disordered SiO2 exhibits cathodoluminescence, with an overall intensity that varies with incident electron beam energy and current density, sample temperature, exposure time, and wavelength. A simple model based on the defect density of states—used to explain electron transport in highly disordered insulating materials—has been extended to predict the relative cathodoluminescent intensity and spectral radiance for disordered SiO2 as a function of these variables. The spectral radiance exhibited four distinct bands, corresponding to four distinct energy distributions of defect states within the band gap; each showed different temperature dependence. These localized defect or “trap” states …
